The present invention relates to a method and apparatus for mounting electronic components onto a circuit board. More particularly, the invention relates to an electronic component mounting method and apparatus that makes it possible to mount such electronic components as IC chips having narrow pitched bumps onto a circuit board by performing a flip chip bonding method.
As electronic component mounting methods of this type, there have conventionally been known various methods. As an example of a conventional electronic component mounting method corresponding to the flip chip bonding method, is a method including steps of temporarily bonding a plurality of electronic components onto a circuit board and thereafter subjecting the electronic components collectively to reflow soldering, thus achieving electronic component mounting, (hereinafter, described as a collective reflow mounting method) as shown FIGS. 22A-22D.
As shown in FIG. 22A, solder paste is fed by printing or the like onto pads 84a, which are a plurality of electrodes on a top surface of a plate-like circuit board 84, so that solder portions 82 are formed on the pads 84a of the circuit board 84, respectively.
Next, in FIG. 22B, an electronic component 81, to which solder bumps 81b are bonded at a plurality of electrodes 81a provided on a bonding surface of the electronic component 81, is sucked and held at its rear surface, which has no electrodes 81a thereon, by a tool 83. After a positional alignment that makes the solder bumps 81b of the electronic component 81 bondable with the solder portions 82 on the circuit board 84, respectively, the solder bumps 81b of the electronic component 81 are pressed against the solder portions 82 of the circuit board 84, respectively, thereby achieving their temporary bonding. For mounting of a plurality of electronic components 81 onto the circuit board 84, these working steps are iteratively performed so that respective electronic components 81 are mounted onto the circuit board 84. It is noted here that the terms, “temporary bonding,” refer to a bonding process such that the electronic component 81 and the circuit board 84 are releasable from their bonding by applying external force to the electronic component 81 or the circuit board 84 without breaking the electronic component 81 or the circuit board 84.
Thereafter, the circuit board 84, to which the electronic components 81 have been temporarily bonded, is conveyed to a reflow soldering working section. As shown in FIG. 22C, the electronic components 81 and the circuit board 84 are heated by a heat source in the reflow soldering working section, by which the solder portions 82 and the solder bumps 81b are melted. In a case where a plurality of electronic components 81 are temporarily bonded to the circuit board 84, those electronic components 81 are collectively subjected to heat so as to melt the solder in this reflow soldering working section.
Thereafter, as shown in FIG. 22D, with the circuit board 84 removed from the reflow soldering working section, molten solder is cooled and solidified, thereby achieving primary bonding of the electrodes 81a of each electronic component 81 to the pads 84a of the circuit board 84, respectively, via the solder, by which the electronic components 81 are collectively mounted onto the circuit board 84. It is noted here that the terms, “primary bonding,” refer to a bonding process that is performed by melting the solder with heat applied to the temporarily bonded electronic component 81 and circuit board 84, and by thereafter solidifying the solder, and this makes it hard to release a resulting bonded state by applying external force to the electronic component 81 or the circuit board 84.
In such a collective reflow mounting method, a multiplicity of electronic components 81, after their temporary bonding, can be subjected to collective melting of solder, by which the electronic components 81 can be finally bonded and thereby mounted to the circuit board 84. This allows for electronic-component mounting operations to be efficiently achieved. As a result, it has been a case in that costs of mounting the electronic components 81 onto the circuit board 84 can be reduced.
However, for such a method, which includes steps for temporarily bonding of the electronic components 81 to the circuit board 84, and thereafter performing their primary bonding by melting the solder, there is a need for conveying the circuit board 84, to which the electronic components 81 have been temporarily bonded, to the reflow soldering working section. During this conveyance, a bonding position of each electronic component 81 relative to the circuit board 84 might be shifted due to vibrations or the like caused by the conveyance, in which case reflowing of the solder in such a shifted state might result in defective bonding of the electronic components 81 to the circuit board 84. Such shifts of the bonding positions as would occur in the collective reflow mounting method would not matter for electronic components to which high precision for their bonding positions is not required, such as general-purpose electronic components. However, for some electronic components, such as IC chips, to which particularly high precision for their bonding positions is required, this would matter.
As an example of a conventional electronic component mounting method corresponding to a flip chip bonding method intended to solve such issues of the collective reflow mounting method as described above, a method including the step of simultaneously heating and pressing electronic components onto a circuit board to thereby subject the electronic components individually to reflow soldering, thus achieving electronic component mounting, (hereinafter, described as a conventional local reflow mounting method) is shown FIGS. 23A-23D.
As shown in FIG. 23A, solder paste is fed by printing or the like onto pads 94a, which are a plurality of electrodes on a top surface of a plate-like circuit board 94, so that solder portions 92 are formed on the pads 94a of the circuit board 94, respectively.
Next, as shown in FIG. 23B, an electronic component 91 to which solder bumps 91b are bonded at a plurality of electrodes 91a provided on a bonding surface of the electronic component 91, is sucked and held at its rear surface, which has no electrodes 91a thereon, by a tool 93. After performing a positional alignment that makes the solder bumps 91b of the electronic component 91 bondable with the solder portions 92 on the circuit board 94, respectively, the solder bumps 91b of the electronic component 91 are, while heated, pressed against the solder portions 92 of the circuit board 94, respectively, by which the solder portions 92 and the solder bumps 911b are melted.
Next, as shown in FIG. 23C, while solder is maintained in a molten state, suction and holding of the electronic component 91 by the tool 93 is released. As a result of this, a self alignment effect by surface tension of the molten solder is obtained.
Thereafter, as shown in FIG. 23D, by solidifying the molten solder, the electrodes 91a of the electronic component 91 are bonded to the pads 94a of the circuit board 94, respectively, via the solder, by which the electronic component 91 is individually mounted onto the circuit board 94. In addition, for mounting of a plurality of electronic components 91 onto the circuit board 94, these working steps are iteratively performed so that respective electronic components 91 are mounted onto the circuit board 94, individually.
In such a local reflow mounting method, the electronic component 91 is sucked and held by the tool 93, the solder bumps 91b of the electronic component 91 are pressed against the solder portions 92 of the circuit board 94 while the solder bumps 91b and the solder portions 92 are heated, respectively, by the tool 93, and thereafter suction and holding of the electronic component 91 by the tool 93 is released while the solder is in the molten state. As a result, a self alignment effect by the surface tension of the molten solder is obtained. Thus, even with more or less poor precision of a bonding position of the electronic component 91 by the tool 93, a precision of a bonding position that would not result in defective bonding eventually could be obtained by the self alignment effect.
However, in a case of high-end electronic components of narrowed bump pitches, from among such electronic components as IC chips, with their bump pitch being as narrow as, for example, not more than 150 μm, it is required for electronic components having bumps of such narrow pitches to meet a high precision for a bonding position of, for example, ±5 μm, which would concern a bonding-position shift amount of an electronic component due to a vacuum break blow occurring at releasing of the suction and holding of the electronic component during solder melting, more than the self alignment effect would be concerned in the local reflow mounting method. Therefore, the above-described electronic component mounting performed by the local reflow mounting method, in which suction and holding of an electronic component by the tool is released during a solder's molten state, has had an issue of incapability of mounting high-end electronic components which have bumps of such narrow pitches as shown above and to which high precision for a bonding position is required.
Accordingly, an object of the present invention is to solve the above-described issues and provide an electronic-component mounting method and apparatus which are capable of mounting high-end electronic components having narrow-pitch bumps, and moreover, which are intended for mounting of electronic components onto a circuit board on which general-purpose electronic components and high-end electronic components are to be mixedly mounted. The method and apparatus allow both productivity and quality to be satisfied by changing a method to be used for individual electronic components depending on precision of a bonding position required for individual electronic components.